In the past, fasteners for attaching railroad rails to support structures have included a track plate secured to the bottom of each rail by suitable clamping devices, together with an underlying layer of elastomeric material abutting the support structure directly or abutting a second underlying plate which rests on the support structure. Ordinarily, the track and underlying plates on which the rail rests are secured to the support structure by bolts or other clamping arrangements. In certain clamping arrangements of this sort, as exemplified by U.S. Pat. No. 3,784,097, the clamps take the form of clips having a load bearing surface which mate to and overlie the lower rail flange and are secured to an underlying plate by means of bolts. Serrations may be provided in the top surface of the track plate for receiving a projection of the clip to permit lateral adjustment of the clip while limiting horizontal or sideways movement of the clip and rail. Such fasteners are limited to attaching rails that are perpendicular to the longitudinal axis of the track plate or are spaced apart to accommodate separate fasteners for each rail. Sufficient distance between the rails is required to accommodate the track plate of the individual fasteners.
However, rails are not always perpendicular to the track plate and in other cases, the rails are spaced too close together to allow for separate fasteners for each rail. Furthermore, two nonparallel rails may require support on one track plate. Such rails are generally found in systems used to switch trains from one set of rails to another including crossings, switches, frogs and the like. Conventional fasteners may be used in switches on converging rails until the rails are too close together to allow for individual fasteners to be placed under each rail.
Although the fasteners as described are adjustable along the longitudinal axis of the track plate, they fail to provide angular adjustment for nonperpendicular positioning of the rail to the track plate. That is, if other than a substantially perpendicular relationship exists between the rail and the track plate, the load bearing surface of the clips will not fully engage the bottom flange of the rail. In other cases where the rails are spaced too close together such that the usual rail fasteners can not be used for each rail. Hence it is desirous to have a rail fastener that can accommodate lateral and angular adjustments as well as close spacing of rails.
A commercially available product overcoming some of the above described problems is an adjustable special track fastener sold by Lord Corporation, assignee of the present patent. The special track fastener includes a long flat rectangular track plate for attachment to the flanges of more than one rail and has an elastomeric member bonded the length of the track plate on the side opposite to the rail contact side for isolating and damping vibration of the track fastener. Combination of the long track plate and elastomeric member allows for positioning the plurality of rails along the longitudinal length of the track plate. Vertical serrations extend along each of the longitudinal edges of the track plate and are adapted to cooperate with fastener assemblies for securing the plurality of rails to the track plate. The fastener assemblies include a clamping member overlying the flange of each rail and a threaded nut having mating vertical serrations thereon engagable with the serrations along the longitudinal edges of the track plate. The clamping member overlies the nut and has a load bearing surface engagable with the flange of the associated rail. A bolt extends through the clamping member and is threaded into the nut for securing the clamping member to the nut while securing each rail against horizontal movement.
The fastener assembly may be located or adjusted along the longitudinal length of the track plate by virtue of the mating of the vertical serrations of the nut and the track plate. By virtue of the fact that the clamping member may rotate above the aforesaid bolt, it can be used in positively engage the rail along its length regardless of the angular attitude of the rail with respect to the plate. Such rotation provides angular adjustment of the clamping member to positively engage the rail along its length at non-perpendicular displacement of the rail with respect to the track plate.
Furthermore, the clamping member of the fastener assembly has elongated bores there through for the bolts to accommodate the varying distances between the bolts resultant from the angular adjustment of the clamping member. The distance between the bolts is shortest when the rail is perpendicular to the track plate and the distance increases with the nonperpendicularity of the rail.
While the described special trackwork fastener satisfactorily fastens closely spaced or nonparallel rails, hereinafter referred to as special rails, problems have arisen in using the fastener. One problem area is the adaptation of the special trackwork fastener to various separation widths between the rails. As one can imagine, widths between the rails will vary based on the point of convergence of the rails. Such separation widths may vary from about 1 inch to about 12 inches. Using a long special trackwork fastener for a short separation results in much of the special fastener being unused. Varying the length of the special trackwork fastener requires manufacturing using various molds corresponding to the length of the fasteners.
The resiliency properties of the special trackwork fastener are less desirable than the regular single pad under a single rail. Bonding of rubber to the full length of the track plate results in a very stiff fastener, increasing the spring rate of the elastomeric member underneath the rail and decreasing the flexibility of the fastener. Also, bonding of the rubber to the full length of the track plate is more expensive and difficult than for single pads. Various costly large molds are required to make the special fasteners. Serrations along the longitudinal edges of the track plate also increase the cost of the fastener.
The elastomer member of the aforesaid special trackwork fastener may require replacement after a period of time due to normal wear or upon failure. Replacement of the elastomeric member of the special trackwork fastener as described requires replacement of the entire fastener even though a limited portion of the fastener needs replacement. In summary, although the special trackwork fastener is capable of fastening special rails, various undesirable features are inherent in the product.